Data transmission in a radio communication system may be from a first radio station via an air interface.
For conventional joint transmission, e.g. in a radio communication system, a central unit receives data from a backbone network for all connected terminals (e.g. mobile stations), which are simultaneously scheduled to receive the data from radio stations over an air interface, and calculates dependent on the overall channel matrix H an according weighting matrix W—e.g. for zero forcing (ZF) the pseudo inverse of H for pre processing of the data before transmission. The central unit includes the common medium access control (MAC) as well as the MU-MIMO (Multi User-Minimum Input Maximum Output) pre-processing for all radio stations transmitting the data.
A cooperative antenna system based on joint transmission/joint detection, for example the service area concept as described in T. Weber, M. Meurer, W. Zirwas, “Low Complexity Energy Efficient Joint Transmission for OFDM Multiuser Downlinks”, Proc. IEEE PIMRC 2004 Barcelona, Spain, is essentially a distributed MU-MIMO system involving several advantages.
Firstly a cooperative antenna system exploits the free available spatial dimension as well known for all MIMO systems. In case of spatial multiplexing the capacity may be enhanced by factors. MU-MIMO systems have the additional advantage of low cost terminals, e.g. mobile stations, which might be equipped with only one or two antenna elements.
Due to the distributed nature of e.g. the service area concept where several adjacent—but geographically far off placed—radio stations, e.g. base stations, are used as transmit antennas full macro diversity gains are available.
The most important advantage for cellular radio systems is probably the avoidance of inter cell interference (ICI) between radio stations of a service area due to the cooperation in the central unit. In conventional cellular radio communication systems the overall spectral efficiency is significantly decreased compared to the spectral efficiency of a single cell due to the ICI especially at cell border. For a service area with joint transmission ICI increases spectral efficiency even beyond that of a single isolated cell due to rank enhancement, i.e. the number of uncorrelated transmission channels and therefore the rank of the channel matrix increases.
In spite of these many advantages there is still some reluctance to apply such system concepts. One of the main reasons is the required central unit, which would require a hierarchical network structure. The vision of network planers is a flat hierarchy which allows for economy of scale for the hardware of radio stations and which is fast and easily deployable.